Patients with acute respiratory distress syndrome (ARDS) frequently develop atelectasis in dorsal lung regions because of gravity and the compression by the heart and the diaphragm. Since lung perfusion is predominantly distributed in lower lung regions, a reduction of ventilation in these areas results in further ventilation-perfusion mismatch, called shunt. The development of atelectatic lung regions necessitate the use of higher ventilation pressures, which in turn results in excessive transpulmonary pressures and ventilation-induced lung injury in the ventral regions. Therefore it is common to promote the prone position in patients with ARDS in order to improve ventilation-perfusion matching and thus, protect the ventral regions from hyperinflation. In patients with COVID-19-related ARDS, the value of such therapeutic strategy based on placing in prone position has not been completely elucidated. The aims of the study are to determine whether prone positioning improves dorsal regional ventilation when compared to supine position. Moreover, another aim is to assess the changes in intrapulmonary shunt following patient position changes.
